Cloud Seeding By: Julie Walter Air Chem and Pollution

Cloud Seeding

    By: Julie Walter
Air Chem and Pollution

History
• In Kurt Vonnegut’s 1963 novel titled “Cat’s
  Cradle” a young scientist has in his
  possession an ice crystal that has the
  power to freeze any liquid that comes into
  contact with it. This non fiction satire is
  loosely based around Vonnegut’s brother
  Bernard Vonnegut an atmospheric
  scientist who discovered the ability of
  Silver Iodide as an ice nuclei catalyst.

Cloud Seeding is…
• a process that uses a product such as
  Silver Iodide or dry ice released into the
  environment, mostly mountainous regions
  that constantly create clouds, to augment
  the amount of water in the air to create
  precipitation or suppress fog and hail.

2 main types
dynamic- is more commonly used for warm latitude
clouds that are more capable of releasing latent heat to
add the freezing process of the ice nuclei in clouds.
static seeding- involves cumulus clouds traveling west
to east through mountain ranges that are picking up
water and other microscopic particles like soil, dust,
smoke, that then are cooled because of the high
altitudes. As the water or condensation nuclei cool
more, ice nuclei form and grow bigger. Introducing
certain chemicals such as Silver Iodide helps the
condensation nuclei to freeze thus forming more ice
nuclei. This is more common in areas like Colorado

Factors
Specific storm systems are needed to create the ideal
conditions for precipitation. From a mesoscale system the
warmer less dense air is pushed above the colder dense air.
Over a mountain range when pushed up enough the warm air
that is filled with moisture should reach an optimum cooling
point of between -9 to14 degrees Celsius. This is the ideal
temperature window for ice nuclei to form and drop as
precipitation. Other variables include the horizontal and
vertical distribution of clouds plus the lifetime of those clouds.
Winds can form suddenly and blow clouds away from the
targeted area. Some experiments show effectiveness when
location for generators were chosen assuming a mean wind
direction and no wind change, but due to insufficient
knowledge about wind flow systems in cloud liquid water
(CLW) regions data can show positive or negative effects.

Costs for Vail
According to www.vail.com there are 5289 acres
of skiable terrain, not including the resort and
surrounding town. So the reported costs for the
2005 season was about “$165,000 using 17
cloud seeding generators” noted by Larry
Hjermstad, manager for a Durango-based
Western Weather Consultants, whose company
supplied Vail Resorts with the cloud seeding
generators. This comes out to be about $31.20
per an acre.

Implications
“Essentially we cannot tell the difference between a
 snowflake that has come from a silver iodide crystal and
 a snowflake from a natural ice crystal”-Larry Hjermstad
 Although there might be an increase in precipitation from
 tests, the tested snowfall might not even test positive for
 Silver Iodide in targeted areas, data is hard to quantify,
 making cloud seeding an arguable technique.
 Producing more snow in a warmer climate has many
 different outcomes in feedback loops that tie in
 snowmelt, warming temperatures, Pine Beetles, ice-
 albedo relations, and disrupting these could have more
 of an effect than anyone could imagine just like the
 burning of fossil fuels has shown.

In the future…
• Geoengineerists have been working to inject aerosols
  into the stratosphere to control tropospheric pollution.
  This warm cloud seeding technique would enhance
  cloud albedo. There are negative and positive effects to
  this in that acid rain can be created and the sulfur cycle
  would be disturbed, but increased cloud coverage would
  permit cooler temperatures.
• Another proposal by climatologists at the National Center
  for Atmospheric Research for controlled climate cooling
  would be to seed low maritime oceanic clouds with
  seawater particles that would act as condensation nuclei,
  activate more precipitation which would then further
  increase cloud albedo and longevity.

Works Cited
I own all of these photographs

"Seeding and Precipitaion Processes." December 10, 1999.http://www.rap.ucar.edu/staff/vidal/seeding/ (accessed
    11/30/2009).

Westwater, Ed, R. "The accuracy of water vapor and cloud liquid determination by dual-frequency ground based
            microwave radiometry." Radio Science 13, no. 4 (1978): 677-685.

Berwyn, Bob. "Cloud seeding to continue above Vail Mountain." October 6,
    2004.http://www.vaildaily.com/apps/pbcs.dll/article?AID=/20041006/NEWS/110060010 (accessed 11/28/2009).

Rizer, Amy. "Cloud Seeding." November 17,
    2004.http://media.www.collegian.com/media/storage/paper864/news/2004/11/17/Newsregi
    Salazar, VidalonalAndState/Cloud.Seeding-1705556.shtml (accessed 11/31/2009)

Griffith CCM, Don A.. "The Potential Use of Winter Cloud Seeding Programs to Augment the Flow      of the Colorado
      River." For use by the Upper Colorado River Commission 1, no. (2006): [4-12].

Moore, C.B.. "University of Albany Atmospheric Sciences Index."
    1997.http://www.deas.albany.edu/deas/bvonn/bvonnegut.html (accessed 11/31/2009).

Rabson, Diane. "NCAR's assualt on the hail problem: The National Research Experiment." It Happened Here
           June, no. (1999): [1-5].

Rasch, P.J., S. Tilmes, R.P. Turco, A. Robock, L. Oman, C.C. Chen, G.L. Stenchikov and R.R. Garcia. 2008: “An
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    doi: 10.1098/rsta.2008.01031

Latham, J., P. Rasch, C.C. Chen, L. Kettles, A. Gadian, A. Gettelman, H. Morrison, K. Bower and T. Choularton.
             2008: “Global temperature stabilization via controlled albedo enhancement of low-level maritime
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